Increase timeout in a flaky test

`SessionPoolingStressIT` seems to be flaky but never has any worker
threads running after failure. This commit increases the executor
shutdown timeout.

Author: lutovich

driver/src/test/java/org/neo4j/driver/v1/stress/SessionPoolingStressIT.java

@@ -122,7 +122,7 @@ public void shouldWorkFine() throws Throwable
 
         stop.set( true );
         executor.shutdown();
-        assertTrue( executor.awaitTermination( 30, TimeUnit.SECONDS ) );
+        assertTrue( executor.awaitTermination( 90, TimeUnit.SECONDS ) );
 
         Throwable failure = failureReference.get();
         if ( failure != null )